1. Field of the Disclosure
The present disclosure generally relates to shaker screens and methods of forming shaker screens. More specifically, the present disclosure relates to composite frame shaker screens and methods of forming composite frame shaker screens and attaching filtering elements thereto. More specifically still, the present disclosure relates to composite hookstrip shaker screens and methods of forming the same.
2. Background
Oilfield drilling fluid, often called “mud,” serves multiple purposes in the industry. Among its many functions, the drilling mud acts as a lubricant to cool rotary drill bits and facilitate faster cutting rates. Typically, the mud is mixed at the surface and pumped downhole at high pressure to the drill bit through a bore of the drillstring. Once the mud reaches the drill bit, it exits through various nozzles and ports where it lubricates and cools the drill bit. After exiting through the nozzles, the “spent” fluid returns to the surface through an annulus formed between the drillstring and the drilled wellbore.
Drilling mud provides a column of hydrostatic pressure, or head, to prevent “blow out” of the well being drilled. This hydrostatic pressure offsets formation pressures thereby preventing fluids from blowing out if pressurized deposits in the formation are breeched. Two factors contributing to the hydrostatic pressure of the drilling mud column are the height (or depth) of the column (i.e., the vertical distance from the surface to the bottom of the wellbore) itself and the density (or its inverse, specific gravity) of the fluid used. Depending on the type and construction of the formation to be drilled, various weighting and lubrication agents are mixed into the drilling mud to obtain the right mixture. Typically, drilling mud weight is reported in “pounds,” short for pounds per gallon. Generally, increasing the amount of weighting agent solute dissolved in the mud base will create a heavier drilling mud. Drilling mud that is too light may not protect the formation from blow outs, and drilling mud that is too heavy may over invade the formation. Therefore, much time and consideration is spent to ensure the mud mixture is optimal. Because the mud evaluation and mixture process is time consuming and expensive, drillers and service companies prefer to reclaim the returned drilling mud and recycle it for continued use.
Another significant purpose of the drilling mud is to carry the cuttings away from the drill bit at the bottom of the borehole to the surface. As a drill bit pulverizes or scrapes the rock formation at the bottom of the borehole, small pieces of solid material are left behind. The drilling fluid exiting the nozzles at the bit acts to stir-up and carry the solid particles of rock and formation to the surface within the annulus between the drillstring and the borehole. Therefore, the fluid exiting the borehole from the annulus is a slurry of formation cuttings in drilling mud. Before the mud can be recycled and re-pumped down through nozzles of the drill bit, the cutting particulates must be removed.
One type of apparatus used to remove cuttings and other solid particulates from drilling fluid is commonly referred to in the industry as a “shale shaker.” A shale shaker, also known as a vibratory separator, is a vibrating sieve-like table upon which returning solids laden drilling fluid is deposited and through which substantially cleaner drilling fluid emerges. Typically, the shale shaker is an angled table with a generally perforated filter screen bottom. Returning drilling fluid is deposited at the feed end of the shale shaker. As the drilling fluid travels down the length of the vibrating table, the fluid falls through the perforations to a reservoir below thereby leaving the solid particulate material behind. The vibrating action of the shale shaker table conveys the solid particles left behind until they fall off the discharge end of the shaker table. The above described apparatus is illustrative of one type of shale shaker known to those of ordinary skill in the art. In alternate shale shakers, the top edge of the shaker may be relatively closer to the ground than the lower end. In such shale shakers, the angle of inclination may require the movement of particulates in a generally upward direction. In still other shale shakers, the table may not be angled, thus the vibrating action of the shaker alone may enable particle/fluid separation. Regardless, table inclination and/or design variations of existing shale shakers should not be considered a limitation of the present disclosure.
Preferably, the amount of vibration and the angle of inclination of the shale shaker table are adjustable to accommodate various drilling fluid flow rates and particulate percentages in the drilling fluid. After the fluid passes through the perforated bottom of the shale shaker, it may either return to service in the borehole immediately, be stored for measurement and evaluation, or pass through an additional piece of equipment (e.g., a drying shaker, a centrifuge, or a smaller sized shale shaker) to remove smaller cuttings and/or particulate matter.
Because shale shakers are typically in continuous use, repair operations, and associated downtimes, are need be minimized as much as possible. Often, the filter screens of shale shakers, through which the solids are separated from the drilling fluid, wear out over time and subsequently require replacement. Therefore, shale shaker filter screens are typically constructed to be quickly removable and easily replaceable. Generally, through the loosening of several bolts, the filter screen may be lifted out of the shaker assembly and replaced within a matter of minutes. While there are numerous styles and sizes of filter screens, they generally follow similar design.
Typically, filter screens include a perforated plate base upon which a wire mesh, or other perforated filter overlay, is positioned. The perforated plate base generally provides structural support and allows the passage of fluids therethrough, While many perforated plate bases are flat or slightly arched, it should be understood that perforated plate bases having a plurality of corrugated or pyramid-shaped channels extending thereacross may be used instead. Pyramid-shaped channels may provide additional surface area for the fluid-solid separation process while guiding solids along their length toward the end of the shale shaker from where they are disposed.
In typical shakers, a screen or screen assembly is detachably secured to the vibrating shaker machine. With the screen assembly or multiple screen assemblies secured in place, a tray is formed with the opposed, parallel sidewalls of the shaker. The drilling mud, along with drill cuttings and debris, is deposited on the top of the screen assembly at one side. The screen assembly is vibrated at a high frequency or oscillation by a motor or motors for the purpose of screening or separating materials placed on the screen. The liquid and fine particles will pass through the screen assembly by force of gravity and be recovered underneath. The solid particles above a certain size migrate and vibrate across the screen or screens where they are removed.
It is known that to obtain the proper vibration of the screen assembly, slack in the screens must be discouraged. Any slack in the screen produces an undesirable flapping action of the screen, which reduces the effectiveness of the shaker vibration and also results in increased wear of the screen. Accordingly, it is known that the screen should be securely and tightly held down to the vibrating machinery by an attachment mechanism.
One type of attachment mechanism includes hooks on each longitudinal end of the screen assembly to connect to the shaker. The shaker will have a channel-shaped drawbar on each side, which mates with a corresponding hook on the screen assembly. The drawbars are held in place by bolts or other fasteners. These are detachably connected so that the screens may be replaced from time to time. Such screens are referred to in the industry as “hookstrip screens.”
Typically, hookstrip screens are manufactured by first forming a metal perforated plate (i.e., a backplate) which serves as support structure for the screen assembly. The metal perforated plate is often heavy, expensive to manufacture, and blocks a substantial portion of potential screen area. During screen manufacture a screen surface (i.e., a filtering element) is attached to the metal perforated plate with powder epoxy. When the powder epoxy is melted, and the screen surface attached to the metal perforated plate, the epoxy spreads over the screen surface thereby blocking screening surface. The bonding process is also relatively long, in some instances lasting anywhere from 5 to 15 minutes.
Accordingly, there exists a need for a relatively inexpensive hookstrip screen that may provide an effective surface for the screening of drilling fluids. Also, there exists a need to increase the efficiency of the screening process so that downtime may be limited while increasing the rate of screening.